1. Field of the Invention
The present invention relates generally to the field of modem communication systems, and more specifically to the field of data terminal equipment (DTE) command sets.
2. Description of Related Art
During the 1970's, a small communications company called Bizcom developed the concept of adding intelligence to Data Communication Equipment (DCE) using codes, referred to as a command set, that governs the operational capability of the modem. Other modem manufacturers developed similarly performing modems. Unfortunately, during the early days of intelligent modems, the command set built into modems manufactured by different vendors typically were incompatible with each other. Thus, many communications software products originally operated only with a specific modem or a few modems, as determined by the command set for the particular modem.
The Hayes Microcomputer Products series of Smartmodems later captured over 50 percent of the personal computer modem market, and its command set became the de facto industry standard. At present, many modem manufacturers cite their products as being "Hayes compatible", which suggests that the product supports at least some of the Hayes modem command set.
The Hayes command set consists of a basic set of commands and command extensions. The basic commands, such as placing the modem off-hook (which occurs when the telephone handset is lifted from its cradle) and dialing a number are common to Hayes and Hayes-compatible modems. Command extensions, such as placing a modem into a specific operating speed or initiating certain features (including data compression or a specific type of error detection and correction) are applicable only to modems built to transmit and receive data at that speed or modems that support the requested feature.
Other modems, such as the commercially available TrailBlazer from Telebit, employ a command set that essentially is a superset of the Hayes command set. Although communications software that uses the Hayes command set operates with the TrailBlazer modem, such software cannot use the full potential of the modem since the Hayes command set does not support several TrailBlazer modem features. To effectively operate the Telebit TrailBlazer or another modem that incorporates special features, software written specifically to support those modem features is required.
The Hayes command set (referred to as the AT command set) provides intelligence only to the DCE like a modem. This command set governs its operational capability, enabling automatic dialing and redialing of telephone numbers, selection of operating transmission rate, and various other intelligent functions.
However, over the past several years, user expectations have increased and equipment including personal computers, terminals, and computer ports are used as an added source of data communications. These equipment are referred to as Data Terminal Equipment (DTE). The physical, electrical, and logical rules for the exchange of data between DTE's and DCE's are specified by an interface standard. The most commonly used interface standard are the Electronic Industries Association (EIA) RS-232-C and RS 232-D standards. These are similar to the CCITT V.24 standard used in Europe and other locations outside of North America. Both the RS-232-C and the RS-232-D formally specify the use of a D-shaped, 25-pin interface connector. The use of the RS-232-C basically has been universal since its publication by the EIA in 1969.
The RS-232 standard defines the interfacing between DTE's and DCE's in the United States. However, there is no standard command set available for the DTE offering similar operational capabilities to the DCE (intelligent) command set. The DCE typically is a separate entity and, as such, is relatively easy to define. On the contrary, the DTE could be a computer, a terminal, or another intelligent equipment. Thus, it has been difficult to clearly isolate the DTE in an intelligent equipment environment. Once the DTE functional block is abstracted out then there is a need for a system, including a standard command set, for digital communication to this DTE functional block in a DTE environment. A command set embodying the present invention will complement the present DCE standard command set.